Crystallization kinetics and role of stress in Al induced layer exchange crystallization process of amorphous SiGe thin film on glass

摘要

The present study reports Al induced crystallization of amorphous (a)-SiGe in the Al-Ge-Si ternary system with the a-SiGe/Al bilayer structure on glass at low temperature similar to 350 degrees C. The origin of the Al induced layer exchange (ALILE) mechanism that occurs in the a-SiGe/Al system is investigated by studying the crystallization kinetics as well as the evolution of stress in the Al layer during the crystallization process. The growth kinetics was analyzed using Avrami's theory of phase transformation as the crystallization occurs under isothermal condition. It shows that initial growth of the polycrystalline (poly)-SiGe phase follows a 3D mode, characterized by n similar to 3, where n is the Avrami constant. It then switched over to a 2D mode through an intermediate explosive growth as the crystallization fraction increases. The stress was evaluated using X-ray diffraction analysis based on multi-hkl sin(2 )psi formalism. A corroboration of the growth kinetics with stress analysis shows that nucleation and growth of the poly-SiGe phase inside the Al layer at 350 degrees C leads to buildup of compressive strain in the Al layer. The increase in strain energy due to compression in the Al layer at elevated temperature is the driving force that initiates the layer exchange process.